Control system for an incineration plant, such as for instance a refuse incineration plant

ABSTRACT

A control system for an incineration plant, comprising an incineration furnace with a combustion path along which the material to be burned is transported, air supply means, a steam generator, and control means with a steam controller and an oxygen controller which, depending on respectively the generated amount of steam and the oxygen in the furnace, generate control signals for adjusting the size and/or speed of a stream of material in the furnace and/or adjusting the air supplied. The control signals control the generated amount of steam to a first adjusting value and via air supplied the amount of oxygen to a second adjusting value. The steam controller controls a summing device which forms a sum signal used which via calculating means modifies the output signals of control circuits controlled by the output signal of the oxygen controller for the air supply to the furnace and/or the size of the supply stream of material to the furnace and the speed of the stream of material through the furnace respectively, to obtain definitive control signals.

This is application is the U.S. National Application NumberPCT/NL00/00713 filed on Oct. 4, 2000, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to a control system for an incineration plant,such as for instance a refuse incineration plant.

SUMMARY OF THE INVENTION

The invention relates to a control system for an incineration plant,such as for instance a refuse incineration plant, comprising anincineration furnace with an inlet for supplying material to be burned,an outlet for discharging burned material, a combustion path extendingbetween the inlet and the outlet, and along which, in use, the materialis transported in a direction of transport from the inlet to the outletfor combustion of the material, and air supply means for supplying airto the combustion path, the incineration plant further being providedwith a steam generator for generating steam by means of heat generatedin the furnace and control means comprising a steam controller and anoxygen controller which, depending on respectively the amount of steamgenerated by the steam generator and the amount of oxygen in thefurnace, generate one or more control signals for adjusting the sizeand/or speed of a supply stream of the amount of material respectivelyto and through the furnace and/or for adjusting the amount of airsupplied to the furnace by means of the air supply means, the controlmeans adjusting the signals such that the steam generator generates anamount of steam per time unit which optimally corresponds with a firstpredetermined adjusting value, and that the air supply means supply suchan amount of air that an amount of oxygen is contained in the furnacewhich optimally corresponds with a second predetermined adjusting value.Such a system is known from practice and is, inter alia, used in therefuse incineration plants built by the firm of Von Roll. One of theproblems occurring during refuse incineration is constituted by thefluctuations in the process caused by the continuously changing refusecomposition. Strong fluctuations in the refuse composition and thus inthe energetic power supplied may result in strong process fluctuations,such as fluctuations in the temperature of the furnace. Such processfluctuations may be harmful to the plant. Also, the process fluctuationsmay involve product fluctuations, such as fluctuations in the amount ofsteam produced or the electricity generated therewith. This has theresult that the yield and quality of these products is reduced. In theknown control system, to provide a solution for the problems described,control means are used which generate the at least one control signal toadjust the size and/or speed of the stream of the amount of materialthrough the furnace and/or to adjust the amount of air supplied to thefurnace by means of air supply means. The control means serve to controlthe at least one control signal such that the above fluctuations aredamped.

The known control means as used in the so-called Von Roll control reducethe above-described problems because the at least one control signal isformed as the sum of a signal provided by a steam controller and asignal provided by an oxygen controller, as a result of which excessoxygen in the furnace and deficient steam oppositely affect the controlsignal and therefore counterbalance each other to a certain degree asfar as the control of the plant is concerned. Nevertheless, the knowncontrol system is not, or not sufficiently, capable of retaining theoutput variables steam and oxygen at the selected adjusting points.

There is therefore a need for an improved control system for anincineration plant. The object of the invention is to meet this need.According to the invention a control system of the above-described typeis therefore characterized in that the output signal of the steamcontroller is supplied to a summing device for forming a sum signal usedto modify via corresponding calculating means the output signals ofcontrol circuits controlled by the output signal of the oxygencontroller for the air supply to the furnace and/or the size of thesupply stream of material to the furnace and the speed of the stream ofmaterial through the furnace respectively, to obtain definitive controlsignals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in more detail with reference tothe accompanying drawings, in which:

FIG. 1 diagrammatically shows an example of a refuse incineration plantprovided with a control device, in which the invention can be used;

FIG. 2 shows a block diagram of a known control device for a refuseincineration plant; and

FIG. 3 shows an example of a block diagram of a control device accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 a possible embodiment of a plant for continuous thermalcombustion of refuse is denoted by reference numeral 1. The plantcomprises an incineration furnace 2 with an inlet zone 4 for supplyingthe refuse to be burned, an outlet zone 6 for discharging the burnedrefuse and a combustion path 8 extending between the inlet and theoutlet, and along which, in use, the material to be burned iscontinuously transported in a direction of transport from the inlet zoneto the outlet zone, as indicated by an arrow 10. The furnace is furtherprovided with transport means 12, which may comprise, for instance, agrate for continuously or stepwise transporting the refuse in thedirection of transport 10.

The system is further provided with air supply means 14 for supplying,preferably heated, air to the combustion path 8. Upstream of the inletzone the furnace is provided with a chute 16 into which the refuse canbe discharged, as indicated by an arrow 17. In the chute 16 there isfurther provided a supply or metering slide 18 which can move forwardand backward between a first position 20 and a dotted second position22. When the chute contains refuse, the supply slide can be moved fromthe first to the second position under control of a signal on line 24 sothat refuse is introduced via the inlet zone 4 into the combustion path8. Subsequently, the supply plate moves back to the first position. Whenreturned to the first position, the supply plate can move to the secondposition again, if desired, to push more refuse into the furnace.

The furnace is further provided with a chimney 26 and a diagrammaticallyindicated heat exchanger which functions as steam generator 28, andwhich uses the heat developed in the furnace to generate steam. With thesteam, for instance a turbine 29 can be driven, which in turn can drivea current generator 30.

The furnace is further provided with an inlet means 23 for controllablysupplying secondary air 25.

In use, the furnace is therefore filled with refuse by means of themetering slide 18. This refuse is then moved slowly in the direction oftransport by means of the transporting means 12. When the refuse isstill in the furnace near the inlet zone, the refuse will be heated andevaporation will take place. The heating occurs partly because thefurnace is already very hot through combustion of earlier suppliedrefuse and can be further promoted by supplying heated air by means ofthe air supply means 14. When the waste is further transported in thedirection of transport, the refuse reaches the so-called main combustionzone. Here the major part of the refuse will burn. Subsequently, therefuse will be further transported in the direction of the outlet 6. Thefire will then slowly become extinguished, and final combustion isreported. Eventually, the burned refuse will leave the furnace via theoutlet 6. Because the heating value of the refuse can vary, the heatproduction in the furnace and thus the generation of steam and theconsumption of oxygen can also strongly vary. To compensate for theinfluence of a variable heating value of the refuse, the system isfurther provided with a control device 31.

In this example the control device 31 is connected with the steamgenerator 28 via a line 32. However, the control device may also beconnected with the current generator 30. The steam generator 28generates on line 32 a signal which is a measure of the amount of steamgenerated by the steam generator 28. Furthermore, via a line 34 a firstreference signal is supplied to the control device 31. This referencesignal has a adjusting value corresponding with the target value of theamount of steam which the steam generator 28 is considered to deliver.The control device 31 compares the signal on line 32 with the signal online 34. When these signals correspond with each other, the steamgenerator 28 generates the predetermined amount of steam. When it turnsout, however, that the generated amount of steam is less than theadjusting value on line 34, the control device 31 generates a firstcontrol signal on line 38. The control signal on line 38 is supplied inthis example to the control unit 40. When it is indicated on line 38that the amount of steam produced is less than the adjusting value online 34, the control unit 40 will control the metering slide 18 via line24 such that more refuse is supplied to the furnace, which has theresult that somewhat more refuse will burn and that the steam productiontherefore increases. When it subsequently turns out that the steamproduction actually reaches the adjusting value, the signals on lines 32and 34 will become equal to each other and the control signal on line 38generated by the control device 31 will go to zero again. Now thecontrol unit 40 knows that the steam production is at the right leveland will control the supply plate 18 via line 24 such that it keepssupplying refuse to the furnace at the increased speed. Further, becausemore refuse is supplied to the furnace, the control unit 40 will in thisexample increase the speed of the transport means 12 accordingly via aline 42. Per time unit more refuse is therefore passed through thefurnace.

When the heating value of the refuse supplied to the furnace increases,the signal on line 32 will indicate that the steam generator 28generates accordingly more steam. When thus more steam is generated thancorresponds with the predetermined adjusting value on line 34, thecontrol device 31 will generate on line 38 a signal negative in thisexample. The control unit will control the supply plate 18 in responsethereto such that per time unit less refuse is supplied to the furnace.Also, via line 42 the rate of transport of the refuse through thefurnace will be reduced accordingly. The above reductions will becarried out such that eventually on line 32 a signal is generated whichcorresponds with the adjusting value on line 34. This means that in thatcase the amount of steam generated by the steam generator 28 is equal tothe predetermined adjusting value. The control unit is arranged suchthat a signal of the steam generator also affects the air supply, aswill be apparent from the following.

In this example the control device 31 is further connected via a line 46with an oxygen sensor 48, which in this example is located behind thesteam generator, which oxygen sensor 48 detects the amount of oxygen inthe furnace and provides a signal which is a measure of the amount ofoxygen in the furnace.

Via a line 52 a second reference signal having a second adjusting valueis supplied to the control device 31. This second adjusting valueindicates the target value of the amount of oxygen considered to bepresent in a furnace. If, however, it turns out that the furnacecontains more oxygen than corresponds with the second adjusting value,the control device 31 will generate on line 54 a signal which has theresult that the control unit 40 controls the air supply means via a line56 such that the amount of air supplied to the furnace decreases. Such asituation may occur for instance when refuse having a lower heatingvalue is supplied to the furnace. Less oxygen is consumed, so that it isnot necessary to supply excess air to the furnace. If it then turns outthat a reduced supply of the amount of air causes the amount of oxygenin the furnace to decrease again to a value corresponding with thesecond adjusting value on line 52, the control device 31 will in thisexample generate on line 54 a signal having the value 0. At this signalthe control unit 40 will maintain unchanged the amount of air suppliedto the furnace by means of the air supply means 14. Quite analogously,the control device 31 will ensure that when the amount of oxygen in thefurnace falls to below the second adjusting value, the amount of airsupplied to the furnace by means of the air supply means 14 will beincreased again until the amount of oxygen in the furnace correspondswith the second adjusting value again. The control unit is arranged suchthat a signal of the oxygen sensor also controls the metering slide andthe rate of transport, as shown in FIG. 2.

FIG. 2 shows a block diagram of a known type of control device for arefuse incineration plant. The control device shown is standard used inVon Roll refuse incineration plants and is also designated as standardVon Roll control device. The device 60 shown comprises a steamcontroller 61 of the proportional and integrating type (PI controller)and an oxygen controller 62 of the proportional type (P controller). Thecontrollers 61 and 62 receive input signals each formed from thedifference between respectively a steam reference signal 63 and anoxygen reference signal 64, on the one hand, and respectively a signal65 representing the amount of steam and a signal 66 representing theamount of oxygen in the furnace, on the other hand. To form thedifference signals, suitable summing devices 67, 68 are provided.

The steam controller 61 and the oxygen controller 62 each form an outputsignal. These output signals are added in a summing device 69 andsupplied to a number of control circuits of the proportional type. Inthis example three control circuits are used, that is to say a firstcontrol circuit 70 for controlling the primary air supply, a secondcontrol circuit 71 for controlling the movement of the metering slide,and a third control circuit 72 for controlling the rate of transport ofthe material to be burned on the grate for the material to be burned.

The control circuits form control signals which are each added to anoutput signal representing the working point value of the controlsignals. To this end, there are provided summing devices 73, 74, 75 andcalculating means 76, 77, 78 for calculating the working point values ofthe control signals for the primary air, the metering slide, and therate of transport.

The calculating means calculate the working point values starting fromthe steam reference signal supplied to the calculating means via a line79, 80. The calculating means may further be provided with inputs forinputting adjusting constants C2, C3, C4.

The output signals of the summing devices 73. 74, 75 form the eventualcontrol signals U_(pl). U_(do), U_(ro) for the primary air, the meteringslide, and the rate of transport. The control signals are supplied toknown per se control means such as valves, motors etc., not shown.

There are further provided calculating means 81 which calculate thedesired value of the total amount of air starting from the steamreference signal 63 supplied via line 79 and, if required, of aadjusting value C1.

The output signal of the calculating means 81 is reduced in a summingdevice 82 by a signal 83 representing the measured total amount ofprimary air, so that as a result a control signal U_(sI) for thesecondary air is obtained.

FIG. 3 diagrammatically shows an example of an improved control device90 according to the invention. In FIG. 3 parts of the control devicewhich correspond with parts of the control device of FIG. 2 areindicated by the same reference numerals. The control device of FIG. 3differs from that of FIG. 2 in that the output signals of the steamcontroller and the oxygen controller are not added to each other.Moreover, the oxygen controller 91 is designed as PI control, the outputsignal of which controls the control circuits 70, 71 and 72.

The output signal of the steam controller 61 is supplied via a line 92to a summing device 93 to which is also supplied the steam referencesignal 63 via line 79. The summing signal of the steam control signaland the output signal of the PI steam controller is supplied again tothe calculating means 76, 77, 78 and 81.

It is noted that after the foregoing modifications are obvious to thoseskilled in the art. Thus the described control device could also operateon the basis of a current signal with associated current referencesignal, which current signal represents the current generated by acurrent generator, such as for instance the generator 30 of FIG. 1.Also, if desired, an oxygen controller of the P type could be used if anon-optimum control is acceptable. Furthermore, the control means forthe metering slide and the rate of transport could be fixedly coupledtogether, so that only one combined control signal is required toreplace the signals U_(do) and U_(ro).

Furthermore, the reference values for respectively the steam controllerand the oxygen controller can be manually adjustable and/or adjustablethrough a safety device. Also, the control device can be implementedaccording to software and comprise a programmable control device, suchas for instance a computer.

These and similar modifications are deemed to fall within the scope ofthe appended claims.

What is claimed is:
 1. A method for controlling a refuse incinerationplant provided with a steam generator, wherein signals are generatedwhich represent the amount of oxygen in the furnace of the incinerationplant and the amount of generated steam, and wherein target values forthe amount of oxygen in the furnace and the amount of generated steamare adjustable and difference signals representing the differencebetween the target values and the generated values are formed,characterized in that the difference signal representing the differencebetween the target value for the generated steam and the correspondingadjusting value is subjected to an integrating treatment and is added tothe target value for the generated steam and that the thus obtained sumsignal is used to modify a number of control signals for the plant, toobtain definitive control signals.
 2. A refuse incineration plantaccording to claim 1, characterized in that a signal representing thedifference signal with respect to the oxygen in the furnace is subjectedto an integrating treatment.
 3. A refuse incineration plant according toclaim 1, characterized in that the definitive control signals compriseat least one control signal for the air supply to the furnace, as wellas a control signal affecting the material transport through thefurnace.
 4. A control system for an incineration plant, such as forinstance a refuse incineration plant, comprising an incineration furnacewith an inlet for supplying material to be burned, an outlet fordischarging burned material, a combustion path extending between theinlet and the outlet, and along which, in use, the material istransported in a direction of transport from the inlet to the outlet forcombustion of the material, and air supply means for supplying air tothe combustion path, the incineration plant further being provided witha steam generator for generating steam by means of heat generated in thefurnace and control means comprising a steam controller and an oxygencontroller which, depending on respectively the amount of steamgenerated by the steam generator and the amount of oxygen in thefurnace, generate one or more control signals for adjusting the sizeand/or speed of a supply stream of the amount of material respectivelyto and through the furnace and/or for adjusting the amount of airsupplied to the furnace by means of the air supply means, the controlmeans adjusting the control signals such that the steam generatorgenerates an amount of steam per time unit which optimally correspondswith a first predetermined adjusting value, and that the air supplymeans supply such an amount of air that an amount of oxygen is containedin the furnace which optimally corresponds with a second predeterminedadjusting value, characterized in that the output signal of the steamcontroller is supplied to a summing device for forming a sum signalwhich is used to modify via corresponding calculating means the outputsignals of control circuits controlled by the output signal of theoxygen controller for the air supply to the furnace and/or the size ofthe supply stream of material to the furnace and the speed of the streamof material through the furnace respectively, to obtain definitivecontrol signals.
 5. A control system according to claim 4, characterizedin that the oxygen controller is a proportional and integratingcontroller.
 6. A system according to claim 4, characterized in that thesteam controller is replaced by a corresponding controller for aparameter equivalent to the amount of steam produced.
 7. A controlsystem according to claim 6, characterized in that the steam generatordrives a current generator via a turbine and that as correspondingcontroller a current controller is used which reacts to the amount ofelectric current produced by means of the steam produced.
 8. A controlsystem according to claim 4, characterized in that the controls systemis designed at least partly as software, which part designed a software,in operation, controls the incineration plant by means of a programmabledevice.
 9. A control system according to claim 4, characterized in thatthe adjusting values are manually adjustable.
 10. A control systemaccording to claim 4, characterized in that the adjusting values areadjustable by a safety device.
 11. A refuse incineration plant,characterized by a control system according to claim
 4. 12. A refuseincineration plant according to claim 11, characterized in that thecontrol signals are formed starting from the difference between a targetvalue for the amount of oxygen in the furnace and the actual value ofthe amount of oxygen in the furnace.
 13. A refuse incineration plantaccording to claim 11, characterized in that the definitive controlsignals comprise at least one control signal for the air supply to thefurnace, as well as a control signal affecting the material transportthrough the furnace.